The present disclosure is in the technical field of automotive exhaust gas emissions measurement and analysis and the measurement of the energy efficiency of vehicles. More specifically, it is in the field of predicting the exhaust gas emissions of vehicles with Internal Combustion Engines (ICEs), including the emissions from Hybrid Electric Vehicles (HEVs) and predicting the energy efficiency of vehicles for all powertrain types operating in the real world, based on simulating real-world conditions during laboratory testing.
Modern automobiles with ICEs can operate reliably under almost any combination of environmental, road grade, and driving conditions found on Earth. Such vehicles are common throughout the world and operate regularly and reliably in ambient temperatures ranging from well below 0 C to more than 40 C, from dry desert conditions to humid rainforests, and in bumper-to-bumper, slow city traffic to high speed operation on the German Autobahn.
Many countries that host large numbers of automobiles have exhaust gas emissions standards, i.e. “tailpipe” standards that auto manufacturers must comply with. But experience has shown that it is difficult and expensive to test vehicles under the broad range of real-world environmental, road, and driving conditions that are known to affect emissions and fuel economy of vehicles in the real world. And it is well known that the energy efficiency of HEVs and the range of BEVs on a single charge decrease at lower ambient temperatures.
Laboratory-based tailpipe emissions testing has been historically performed under a limited range of ambient conditions, vehicle speed patterns, and driving conditions. Because the number of vehicles has increased dramatically in recent years worldwide, and because vehicles have become increasingly computer-controlled, it has become necessary for governments and automobile manufacturers to better understand the emissions of vehicles across a wider range of operating conditions so that National Ambient Air Quality (NAAQ) standards can continue to be met in current ambient air “attainment areas” and can eventually be met in current “non-attainment areas.” It has also become necessary for vehicle manufacturers to be able to assess the effects of changes to vehicle emission controls and powertrain calibrations across a wider range of ambient and operating conditions.
New vehicle exhaust gas emissions regulations are driven, in part, by measured levels of NAAQ for specific criteria pollutants that are known to directly or indirectly affect human health and for the control of greenhouse gas emissions. NAAQ levels vary widely throughout the world, depending on both mobile emissions sources and stationary sources of pollution. Population densities, weather conditions, vehicle emissions performance, the age and makeup of the local in-use vehicle fleet, stationary sources of air pollution, and geographic features, are all factors affecting NAAQ. For example, the air quality in Southern California can be particularly poor because of a high population density, combined with a well-known atmospheric temperature inversion due to geographic features and atmospheric conditions.
Automobiles and trucks with ICEs contribute to the overall pollution from “mobile sources,” most notably from “tailpipe emissions.” And BEVs contribute to “stationary sources” of pollution, i.e. emissions from electrical power plants. The tailpipe emissions and energy efficiency of any particular vehicle operating in the real world is dependent on many factors, including various environmental conditions, road grade, driver behavior, traffic conditions, and the effectiveness of the vehicle's emissions controls related to those factors.
BEVs may become a significant factor of overall pollution from “stationary sources” in the future if they are produced in increasingly larger numbers because they get their energy from the power grid. Therefore, it is important to understand the energy efficiency of BEVs in real-world driving as well.
The promulgation of new emissions standards for controlling criteria pollutant and greenhouse gas emissions from vehicles with ICEs has been traditionally linked to a laboratory-based testing regime and related methodologies because laboratory-based testing can be very repeatable and because mass-based, real-world (i.e. on-road) testing had not been possible until recently, i.e. since the commercialization of Portable Emissions Measurement Systems (PEMS).
While laboratory testing methods are known to be very accurate and repeatable for emissions measurements under actual test conditions, real-world driving can subject a vehicle to a wide range of conditions that traditional laboratory testing protocols would not. There are many reasons for this, including the difficulty of simulating the full range of real-world temperature and atmospheric pressure conditions in the laboratory, the effects of real-world driver behavior under actual traffic conditions, etc.
To address the limitations of a laboratory-only testing regime for ICE vehicles, PEMS apparatuses and methods for conducting accurate, real-world testing of exhaust gas mass emissions and fuel economy from moving vehicles while they are driven in the real world have been developed. This has become increasingly important in understanding vehicle emissions that affect NAAQ, greenhouse gas emissions, and a vehicle's fuel economy.
Over the past 20 years, PEMS has become a commercial product widely used by both regulators and automobile manufacturers. For example, PEMS-based, real-world testing has become a required test methodology for the vehicle certification process in the European Union, starting in 2017. But laboratory testing continues to be a valuable tool for vehicle manufacturers during the vehicle development process and for regulators because the testing protocols produce very repeatable test results. For example, the effects on tailpipe emissions of large and small changes to a vehicle or powertrain can be precisely determined by repeat tests after introducing such changes.